Pharmacology and drug discovery for T-type calcium channels.

Voltage-gated calcium channels are found in the plasma membrane of many excitable and non-excitable cells. When open, they permit influx of calcium, which acts as a second messenger to initiate diverse physiological cellular processes. Ten unique alpha1 subunits, grouped in three families (CaV1, CaV2, and CaV3), encode biophysically and pharmacologically distinct low-voltage-activated T-type and high-voltage-activated L-type, N-type, P/Q-type, and R-type calcium channels. T-type calcium channels are found in neurons where they generate low-threshold calcium spikes and influence action potential firing patterns, in heart cells where they influence pacemaking and impulse conduction, in smooth muscle cells where they regulate myogenic tone and proliferation, in endocrine cells where they regulate hormone secretion, and in sperm where they regulate the acrosome reaction. Validation of T-type calcium channels in disease is based on an abundance of data pertaining to clinical efficacy of T-type calcium channel blockers in certain human conditions as well as information relating to the distribution, functional properties, and physiological roles of these channels. This review focuses on the cellular and molecular pharmacology of T-type calcium channels. It describes novel research approaches to discover potent and selective T-type calcium channel modulators as potential drugs for treating human disease and as tools for understanding better the physiological roles of T-type calcium channels.